Process for producing nodular cast iron



United States Patent l 8 ,7 PROCESS FOR PRODUCING NODULAR CAST IRON Henning J. Christensen, Addison, lll., assignor to Petrocarb, Inc., New York, N.Y., a corporation of Delaware ware N0 Drawing. Filed Jan. 6, 1964, Ser. No. 336,063 8 Claims. (Cl. 75-130) The present invention relates to the treatment of cast iron and more particularly to'the production of nodular cast iron.

It is well known in the art that various cast irons can be treated to substantially improve the physical properties thereof by (a) the removal of sulphurous contaminants, (b) the addition of small amounts of magnesium and/or other additives, and, (c) the conversion of flake form, .uncombin'ed graphitic inclusions to nodular or essentially spheroidal form.

A general process for producing nodular cast iron, i.e. cast iron comprising nodular or spheroidal uncombined graphitic inclusions, comprises in its broadest aspect supplying to a molten bath of cast iron a relatively minor amount (based on the weight of cast iron to be treated) of magnesium. Such magnesium additions to molten cast iron lower the sulphur content of cast iron compositions, and, if suflicient magnesium is added, such treatment has the effect of producing in cast iron compositions graphite in spheroidal rather than flake form.

Heretofore, the introduction of elemental magnesium metal to a molten bath of cast iron has been largely avoided because the comparatively low boiling point, high degree of reactivity and low density (relative to the density of the molten cast iron) of magnesium metal causes substantial and expensive losses of magnesium due to flashoff at the surface of the molten bath, whereat said loss is usually indicated by a violent pyrotechnic display. Moreover, the introduction of elemental magnesium into molten iron is usually accompanied by a violent reaction which causes splashing of molten iron, and this factor, along with the pyrotechnic display, constitutes a serious threat to the welfare of personnel and equipment, especially in commercial operations wherein the amount of iron to be treated and hence the amount of magnesium metal required is generally great.

Various efforts have been made to mollify this problem such as alloying the magnesium metal with iron, silicon, nickel or the like prior to introduction thereof into the molten cast iron. Although various degrees of success in lessening the violence of the pyrotechnic display have been obtained in this way, the added expense involved in alloying the magnesium metal is substantial.

In accordance with the present invention, however, these problems have been largely solved.

Accordingly, it is a principal object of the present invention to provide an improved process for the production of nodular cast iron.

It is another object of the present invention to provide a more economical and reliable method for introducing elemental magnesium into molten iron.

It is a further object of the present invention to provide a means for producing nodular cast iron by a continuous process whereby treating agents containing elemental magnesium are substantially continuously injected beneath the surface of a bath of molten cast iron, said bath comprising a reservoir of iron into which there is substantially continuously introduced a stream of iron from a melting furnace, and from which there is substantially continuously discharged treated iron which, when cast, contains Patented Nov. 1 5, 1966 improved nodulization reagents for the production of nodular cast iron.

Other objects of the present invention will in part be obvious and will in part appear hereinafter.

In accordance with the present invention, it was discovered that vastly reduced flash-off of magnesium metal, and therefore increased magnesium recovery results when a mixture comprising a carbonaceous material and magnesium is employed as the nodulizing agent in the production of nodular cast iron. While the mechanism of the phenomenon is not fully understood, it is my belief, although there is no intention to be bound thereby, that fine particles of carbon react with liquid and gaseous magnesium at the temperatures existing in the melt to form magnesium-carbon compounds which are more stable than gaseous magnesium, and that this reaction thus increases the quantity of magnesium taken into solution by the molten iron.

It was further discovered that when a gas fluidized solids injection system is utilized for the introduction of the magnesium metal, the mixture of carbonaceous material and magnesium prevents the plugging of injection tubes.

In addition, it was discovered that a mixture comprising a carbonaceous material and elemental magnesium readily permits continuous employment of the gas-solids injection process due to the action of the carbonaceous material in preventing flash-off of the magnesium. It is pointed out that prior attempts to employ a gas-solids injection process in molten iron have been handicapped by the requirement that only a limited concentration of ele- -mental magnesium in mixture with solids could be used when employing a dense stream of solids in gas, i.e., one pound or more of solids per cubic foot of gas.

Many varieties of carbonaceous materials in which carbon is present predominantly in elemental form are suitable for use in accordance with the present invention although it should be noted that it is greatly preferred that said carbonaceous materials be free of harmful impurities. For instance, bituminous coal, petroleum coke and anthracite are generally suitable materials provided that volatile impurities are substantially removed prior to use and that the sulphur content thereof is low. However, it is obviously far more practical to utilize those materials which can be readily obtained naturally free from harmful impurities. Thus, carbonaceous materials such as gas coke, which is produced by thermal decomposition of natural gas, or synthetic graphite, are preferred for use in the present invention. It should be noted that it is important that the carbonaceous materials be pulverent in form, i.e., that said material pass, substantially in toto, through a 6 Tyler mesh sieve. It is preferred, however, that the carbonaceous material utilized comprise a substantial portion of fines. For instance, pulverant carbonaoeous materials, of which pass through a 6 Tyler mesh sieve and which upon processing in commercial mixing and blending equipment for the purpose of obtaining appropriate magnesium treatment mixtures and upon subsequent passage through injection equipment and transport lines will be caused to break down into smaller carbonaceous particles, about 50% of which would pass through a Tyler mesh sieve, would be preferred. Gas coke is particularly suited for this purpose because it is readily abraded and because its ultimate particle size is normally less than about 1 micron.

In accordance with the present invention, the mixture of carbonaceous material and magnesium is introduced beneath the surface of the molten metal. Many means have been devised for the conveyance and introduction of particulate solids beneath the surface of molten metals. One such means of conveyance is that disclosed in co- 3 pending US. application Serial No. 199,311, filed June 1, 1962, by H. Reintjes et al., now Patent No. 3,230,016. In said application there is disclosed a method of supplying particulate solids beneath the surface of a molten bath which comprises pneumatically conveying particulate solid material by introducing a .gas into the lower portion of a mass of said particulate material maintained in a container under pressure, flowing said materials admixed with said gas downwardly from the container through an annular passage into a connecting conduit, introducing additional gas into said conduit from behind the point of introduction of said material/gas mixture thereinto and finally conducting said particulate mixture under the surface of a molten bath.

The weight ratio of carbonaceous material to magnesium metal is subject to considerable variation. However, ratios between about 9' parts and about 0.5 part by weight of carbonaceous material per part magnesium are found to be generally satisfactory. Preferred, however, are weight ratios in which the ratio of carbonaceous material per part magnesium is between about 4 parts and about 0.5 part. Generally, ratios comprising a carbonaceous material content of greater than about 2 parts per part magnesium yield little or no further improvement in the retardation of pyrotechnic display while ratios of less than about 0.5 part per part magnesium generally yield inferior results.

It should be noted that while my discussion of the present invention has been hereinbefore directed solely to n-odulizing agent compositions comprising elemental magnesium/ carbonaceous material mixtures, certain other materials can be added to said mixtures. For instance, under certain conditions it may be desirable to use a minimum quantity of the carbonaceous material. Thus, in order to maintain close control of thecarbon content of the molten iron. It is desirable to use a mixture comprising magnesium, carbonaceous material and some other relatively harmless substance. In that event, burnt lime containing a minimum of fines is used to replace some of the carbonaceous material in order to maintain a mixture which has the desirable free-flowing characteristics. Burnt lime which passes through a 10 Tyler mesh sieve but not more than 2% of which passes through a 100 Tyler mesh sieve is preferred. Generally, the quantity of lime that can be utilized is not critical. Any mixture of carbonaceous material, lime and magnesium comprising between about and about 85% by Weight lime can be utilized provided that (a) the magnesium/carbonaceous material ratio is within the above prescribed limits and (b) the magnesium concentration in the resulting lime/carbonaceous material/magnesium mixture is not less than about of the total. While particulate burnt lime is preferred, sodium carbonate can also be utilized.

The following are illustrative non-limiting examples:

Example 1 characteristic spectacular pyrotechnic display which cannot be safely observed with the naked eye is in evidence at the location where the injection is performed.

Example 2 This example is a duplicate of Example 1 with the exception that there is injected beneath the surface of the molten metal a mixture comprising about 80% burnt lime all of which passes through a 10 Tyler mesh sieve but Example 3 This example is a duplicate of Examples 1 and 2 with the exception that there is injected beneath the surface of the molten metal a mixture comprising about gas coke all of which passes through a 6 Tyler mesh sieve and 20% elemental magnesium. As in Example 2, about 39 lbs., of the mixture is injected for each ton of iron, which results in the addition of approximately 7.8 lbs. of magnesium per ton of iron. Samples taken from the treated metal are found to contain an average of about 0.06% magnesium. The introduction of this mixture is observed to result in a mild reaction which is easily observed with the naked eye.

Example 4 This example is a duplicate of Examples 2 and 3 with the exception that the mixture injected beneath the surface of the molten metal comprises 60% of said burnt lime, 20% elemental magnesium and 20% of said gas coke. As in Examples 2 and 3, about 39 lbs. of the mixture is injected for each ton of iron, which results in the addition of approximately 7.8 lbs. of magnesium per ton of iron. Samples taken from the treated metal are found to contain an average of about 0.06% magnesium. The introduction of the mixture of magnesium, lime and gas coke is observed to result in a mild reaction which is easily observed with the naked eye.

Obviously, manychanges can be made in the abovedescribed examples and procedure without departing from the scope of the invention. For instance, although gas coke is utilized as the carbonaceous material in the above examples, other cambonaceous materials such as particulate synthetic graphite, commonly utilized as electrode material, are entirely suitable. It should be noted that when the graphitic content of the molten cast iron to be treated is determined to be lower than desired, it is preferred to simultaneously decrease magnesium flash-oft and increase the graphitic content of the metal by utilizing particulate graphite as the carbonaceous material.

Obviously, when gas transport systems are to be used for injecting treating agents into the molten iron, it is preferable that a nonoxidizing gas, such as nitrogen, be utilized in said transport. Also, the use of mixtures of magnesium alloy and carbonaceous materials offer benefits and improvements similar to those obtained with mixtures of elemental magnesium and carbonaceous material and accordingly it is intended that the term elemental magnesium as utilized in the claims presented hereinafter, include within its scope magnesium alloys.

Accordingly, it is intended that the above disclosure be regarded as illustrative and as in no way limiting the scope of the present invention.

What I claim is:

:1. In the process of producing nodular cast iron by treating molten cast iron with magnesium, the improvement which comprises injecting under the surface of the molten iron by means of a pressurized inert gas a freeflowing mixture comprising between no more than about 9 parts by weight and not less than about 0.5 part by weight of predominantly elemental carbon, which will pass, substantially in toto, through no larger than a six Tyler mesh sieve, and about one part by weight of elemental magnesium.

2. The process as set forth in claim 1 wherein burnt lime is substituted for up to 85% of the elemental carbon.

3. The process as set forth in claim 2 wherein the burnt lime will pass through no larger than a Tyler mesh sieve and no less than a 100 Tyler mesh sieve.

4. The process as set forth in claim 1 wherein the elemental carbon is gas coke.

5. The process for producing nodular iron on a continuous basis, wherein a substantially continuous stream of molten cast iron from a melting furnace is received into a molten bath, a substantially continuous stream of molten metal is discharged from said ba-th at approximately the same rate as the stream of molten cast iron enters the treating vessel, and there is injected under the surface of the molten bath by means of a pressurized inert gas, a free-flowing mixture comprising between not more than about 9 parts by Weight and not less than about 0.5 part by weight of predominantly elemental carbon which will pass, substantially in toto, through a six Tyler mesh sieve, and about one part by weight of elemental magnesium.

6. The process as set forth in claim 5 wherein bu-rn lime is substituted for up to 85 of the elemental carbon.

7. The process as set forth in claim 6 wherein the burnt lime will pass through no larger than a 10 Tyler mesh sieve and no less than a 100 Tyler mesh sieve.

8. The process as set forth in claim 5 wherein the elemental carbon is gas coke.

References Cited by the Examiner UNITED STATES PATENTS 2,726,152 12/1955 Eash -130 2,757,082 7/1956 Busby et a1 75-130 2,803,533 8/ 1957 Bieniosek 75-130 X 2,823,989 2/1958 Deyrup et al 75-130 X 2,863,764 12/1958 Spangler et a1 75-130 2,870,004 1/ 1959 Estes et al 75-130 X 2,889,222 6/1959 Kurzinski et a1 75-130 2,906,617 9/1959 Wahl 75-130 X 2,937,084 5/1960 Klepp et a1 75-130 2,988,445 6/1961 Hurum 75-130 X 3,080,228 3/1963 Hale et al. 75-130 3,151,975 10/ 1964 Madaras 75l29 X 3,230,016 1/ 1966 Gilbert et a1. 302-53 DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, H. W. TARRING,

Assistant Examiners. 

1. IN THE PROCESS OF PRODUCING NODULAR CAST IRON BY TREATING MOLTEN CAST IRON WITH MAGNESIUM, THE IMPROVEMENT WHICH COMPRISES INJECTING UNDER THE SURFACE OF THE MOLTEN IRON BY MEANS OF A PRESSURIZED INERT GAS A FREEFLOWING MIXTURE COMPRISING BETWEEN NO MORE THAN ABOUT 9 PARTS BY WEIGHT AND NOT LESS THAN ABOUT 0.5 PART BY WEIGHT OF PREDOMINANTLY ELEMENTAL CARBON, WHICH WILL PASS, SUBSTANTIALLY IN TO, THROUGH NO LARGER THAN A SIX TYLER MESH SIEVE, AND ABOUT ONE PART BY WEIGHT OF ELEMENTAL MAGNESIUM. 